Concepts on the quote, files in the portal

That is their whole job. Hiding them behind the invoice means a customer is approving a number with no idea what they are buying — and a deliverable released before payment is the work given away. Which one a file is decides how it behaves, so nobody has to remember a convention.

The concepts freeze at the moment the customer accepts, down to a fingerprint of each file. When somebody says "that is not the design I signed off", the answer is a record rather than two people's memories — and it can tell a file that was changed from one that was merely replaced.

"Three files ready, available once the invoice is settled" gets an invoice paid. Hiding them entirely reads as the work not being finished, and generates an email instead of a payment.

Handing files over ahead of payment is a decision studios make all the time, and it is recorded as a decision with a name and a date rather than by quietly changing the rule. "We chose to release this on the fourth" and "this was always public" are different facts, and only one of them survives a disagreement.